One aim of this project is to determine the role of calcium ions in the process of triggering neural transmitter release. To this end, isolated rat brain presynaptic nerve terminals will be used to correlate the effects of depolarization on calcium accumulation (measured as net calcium and/or Ca45) and transmitter (norepinephrine and acetylcholine) release. Various drugs such as anesthetics and ganglionic blocking agents will be used in effort to dissociate calcium uptake from transmitter release, and to try to determine the intermediate events in the release process. A second objective is to determine the kinetic and molecular basis underlying the "active" transport of divalent cations across the plasma membrane of nerve and muscle fibers. Considerable evidence, primarily from nerve preparations including isolated presynaptic terminals, indicates that this transport involves an exchange of sodium ions for calcium ions. Kinetic details of this exchange mechanism will be studied in internally dialyzed squid axons and giant barnacle muscle fibers. Calcium and sodium fluxes (using Ca45 and Na22 as tracers) and net tissue cation concentrations will be measured. In addition, the effects of various cations on calcium binding by rat presynaptic nerve terminal membrane fragments will be examined in effort to identify the molecular basis for sodium-calcium exchange.